This invention relates to a camshaft mounting arrangement for a motorcycle and more particularly to an improved camshaft and valve train arrangement for an internal combustion engine.
The advantages of overhead camshaft internal combustion engines are well known. Such engines normally can develop greater horsepowers than engines having other types of valve actuation since the overhead camshaft and more direct valve actuation reduces the weight and number of components in the valve train. The use of overhead camshafts has even further advantages when the individual cylinders of the engine are provided with multiple intake and/or exhaust valves. However, the overhead positioning of a camshaft gives rise to some difficulties in design, assembly and servicing. For example, the camshaft must be journaled for rotation, must be fixed in an axial location and, of course, must be driven. All of these ancillary components tend to complicate the cylinder head structure and in some instances can give rise to an enlargement of the engine. This can present specific problems when the engine is used with a compact vehicle such as a motorcycle.
For example, the use of multiple cylinder internal combustion engines for motorcycles is well known. One popular type of engine arrangement embodies two or more cylinders arranged in an inline relationship. It is possible to make the motorcycle more compact and achieve a better weight balance if the inline cylinders are disposed so that the crankshaft axis is transverse to the longitudinal center of the motorcycle rather than being longitudinally aligned with. However, the previously proposed arrangements for driving and supporting overhead camshafts have tended to increase the length of the engine. When the engine is mounted transversely in a motorcycle, therefore, the increase in length tends to encroach upon the area between the rider's knees. To compensate for this, it has been proposed to move the rider's seat rearwardly on the motorocycle. This has a number of disadvantages in that it may cause an awkward riding position and also may adversely affect the balance of the motorcycle.
It is, therefore, as principal object of this invention to provide an improved camshaft arrangement for an overhead cam engine.
It is another object of the invention to provide an improved and simplified camshaft arrangement for an overhead cam engine which does not increase the length of the engine.
As has been previously noted, with an overhead mounted camshaft, it is necessary to journal the camshaft for rotation and also to provide some form of thrust bearing for axially locating the camshaft. With overhead camshafts of the type previously proposed, the thrust bearing arrangements have been positioned at one or both ends of the camshaft spaced longitudinally beyond the outermost cam lobes. Such an arrangement obviously increases the length of the engine.
It is, therefore, a still further object of this invention to provide an improved bearing arrangement for rotatably journaling and axially locating a camshaft.
It is a further object of this invention to provide a more compact bearing arrangement for the camshaft of an overhead cam internal combustion engine.
In conjunction with overhead camshaft engines having multiple valves per cylinder, it has been the practice to employ a separate cam lobe for actuating each valve. When a multiple number of valves is used, however, this has a tendency to increase the length of the camshaft and it is desirable to insure that the camshaft is journaled in such a manner so as to avoid distortion. That is, when a camshaft is provided with a plurality of cam lobes, it is desirable to insure that adequate bearing arrangements are provided along the entire length of the camshaft. However, devices proposed for such arrangements have lengthened the engine and have increased the complexity of the cylinder head assembly.
It is, therefore, a further object of this invention to provide an improved, simplified and compact bearing arrangement for a multiple value overhead cam internal combustion engine.
As has been previously noted, the provision of overhead camshafts tends to complicate the overall cylinder head construction. Furthermore, it is desirable to provide an arrangement wherein the cylinder head may be tightened such as retorqued without necessitating removal of the camshaft or camshaft supporting components.
It is, therefore, a still further object of this invention to provide an improved bolting and bearing arrangement for an overhead cam internal combustion engine that permits retorquing of the cylinder head hold-down members without removal of the camshafts or camshaft supports.